How far will it fire?
How can you increase the range of your catapult?
How can you alter the firing angle so the boulder will drop over the top of some castle walls instead of hitting the walls?
What other siege machines could you design to bombard and sieze a castle from your enemies?
Leonardo Da Vinci made all sorts of drawings of siege weapons and even submarines for warfare around about 1500AD.
The ancient Greeks, Egyptians and Romans all made amazing mechanical inventions for defence and attack.
It is said that ‘Archimedes’ designed a giant claw which could be lowered down to destroy ships attacking his coastal fortress.